QObject::~QObject () [virtual]

Destroys the object, deleting all its child objects.

All signals to and from the object are automatically disconnected, and any pending posted events for the object are removed from the event queue. However, it is often safer to use deleteLater() rather than deleting a QObject subclass directly.

Warning: All child objects are deleted. If any of these objects are on the stack or global, sooner or later your program will crash. We do not recommend holding pointers to child objects from outside the parent. If you still do, the destroyed() signal gives you an opportunity to detect when an object is destroyed.

Warning: Deleting a QObject while pending events are waiting to be delivered can cause a crash. You must not delete the QObject directly if it exists in a different thread than the one currently executing. Use deleteLater() instead, which will cause the event loop to delete the object after all pending events have been delivered to it.

The ChildPolished event is omitted if a child is removed immediately after it is added. If a child is polished several times during construction and destruction, you may receive several child polished events for the same child, each time with a different virtual table.

Returns a list of child objects. The QObjectList class is defined in the <QObject> header file as the following:

typedef QList<QObject*> QObjectList;

The first child added is the first object in the list and the last child added is the last object in the list, i.e. new children are appended at the end.

Note that the list order changes when QWidget children are raised or lowered. A widget that is raised becomes the last object in the list, and a widget that is lowered becomes the first object in the list.

In this example, the MyWidget constructor relays a signal from a private member variable, and makes it available under a name that relates to MyWidget.

A signal can be connected to many slots and signals. Many signals can be connected to one slot.

If a signal is connected to several slots, the slots are activated in an arbitrary order when the signal is emitted.

The function returns true if it successfully connects the signal to the slot. It will return false if it cannot create the connection, for example, if QObject is unable to verify the existence of either signal or method, or if their signatures aren't compatible.

A signal is emitted for every connection you make, so if you duplicate a connection, two signals will be emitted. You can always break a connection using disconnect().

The optional type parameter describes the type of connection to establish. В частности определяет доставляется ли сигнал слоту немедленно или ставится в очередь. If the signal is queued, the parameters must be of types that are known to Qt's meta-object system, because Qt needs to copy the arguments to store them in an event behind the scenes. Если вы пытаетесь использовать соединение с очередями и получаете сообщение об ошибке

This event handler can be reimplemented in a subclass to receive custom events. Custom events are user-defined events with a type value at least as large as the QEvent::User item of the QEvent::Type enum, and is typically a QEvent subclass. The event is passed in the event parameter.

void QObject::deleteLater () [slot]

Schedules this object for deletion.

The object will be deleted when control returns to the event loop. If the event loop is not running when this function is called (e.g. deleteLater() is called on an object before QCoreApplication::exec()), the object will be deleted once the event loop is started.

Note that entering and leaving a new event loop (e.g., by opening a modal dialog) will not perform the deferred deletion; for the object to be deleted, the control must return to the event loop from which deleteLater() was called.

Note: It is safe to call this function more than once; when the first deferred deletion event is delivered, any pending events for the object are removed from the event queue.

A signal-slot connection is removed when either of the objects involved are destroyed.

disconnect() is typically used in three ways, as the following examples demonstrate.

Disconnect everything connected to an object's signals:

disconnect(myObject, 0, 0, 0);

equivalent to the non-static overloaded function

myObject->disconnect();

Disconnect everything connected to a specific signal:

disconnect(myObject, SIGNAL(mySignal()), 0, 0);

equivalent to the non-static overloaded function

myObject->disconnect(SIGNAL(mySignal()));

Disconnect a specific receiver:

disconnect(myObject, 0, myReceiver, 0);

equivalent to the non-static overloaded function

myObject->disconnect(myReceiver);

0 may be used as a wildcard, meaning "any signal", "any receiving object", or "any slot in the receiving object", respectively.

The sender may never be 0. (You cannot disconnect signals from more than one object in a single call.)

If signal is 0, it disconnects receiver and method from any signal. If not, only the specified signal is disconnected.

If receiver is 0, it disconnects anything connected to signal. If not, slots in objects other than receiver are not disconnected.

If method is 0, it disconnects anything that is connected to receiver. If not, only slots named method will be disconnected, and all other slots are left alone. The method must be 0 if receiver is left out, so you cannot disconnect a specifically-named slot on all objects.

Returns the child of this object that can be cast into type T and that is called name, or 0 if there is no such object. Omitting the name argument causes all object names to be matched. The search is performed recursively.

If there is more than one child matching the search, the most direct ancestor is returned. If there are several direct ancestors, it is undefined which one will be returned. In that case, findChildren() should be used.

This example returns a child QPushButton of parentWidget named "button1":

Returns all children of this object with the given name that can be cast to type T, or an empty list if there are no such objects. Omitting the name argument causes all object names to be matched. The search is performed recursively.

The following example shows how to find a list of child QWidgets of the specified parentWidget named widgetname:

Returns the children of this object that can be cast to type T and that have names matching the regular expression regExp, or an empty list if there are no such objects. The search is performed recursively.

Warning: This function is not available with MSVC 6. Use qFindChildren() instead if you need to support that version of the compiler.

bool QObject::inherits ( const char * className ) const

Returns true if this object is an instance of a class that inherits className or a QObject subclass that inherits className; otherwise returns false.

void QObject::installEventFilter ( QObject * filterObj )

Installs an event filter filterObj on this object. Например:

monitoredObj->installEventFilter(filterObj);

An event filter is an object that receives all events that are sent to this object. The filter can either stop the event or forward it to this object. The event filter filterObj receives events via its eventFilter() function. The eventFilter() function must return true if the event should be filtered, (i.e. stopped); otherwise it must return false.

If multiple event filters are installed on a single object, the filter that was installed last is activated first.

Here's a KeyPressEater class that eats the key presses of its monitored objects:

The QShortcut class, for example, uses this technique to intercept shortcut key presses.

Warning: If you delete the receiver object in your eventFilter() function, be sure to return true. If you return false, Qt sends the event to the deleted object and the program will crash.

Note that the filtering object must be in the same thread as this object. If filterObj is in a different thread, this function does nothing. If either filterObj or this object are moved to a different thread after calling this function, the event filter will not be called until both objects have the same thread affinity again (it is not removed).

A meta-object contains information about a class that inherits QObject, e.g. class name, superclass name, properties, signals and slots. Every QObject subclass that contains the Q_OBJECT macro will have a meta-object.

The meta-object information is required by the signal/slot connection mechanism and the property system. The inherits() function also makes use of the meta-object.

If you have no pointer to an actual object instance but still want to access the meta-object of a class, you can use staticMetaObject.

Changes the thread affinity for this object and its children. The object cannot be moved if it has a parent. Event processing will continue in the targetThread.

To move an object to the main thread, use QApplication::instance() to retrieve a pointer to the current application, and then use QApplication::thread() to retrieve the thread in which the application lives. Например:

myObject->moveToThread(QApplication::instance()->thread());

If targetThread is zero, all event processing for this object and its children stops.

Note that all active timers for the object will be reset. The timers are first stopped in the current thread and restarted (with the same interval) in the targetThread. As a result, constantly moving an object between threads can postpone timer events indefinitely.

A QEvent::ThreadChange event is sent to this object just before the thread affinity is changed. You can handle this event to perform any special processing. Note that any new events that are posted to this object will be handled in the targetThread.

Warning: This function is not thread-safe; the current thread must be same as the current thread affinity. In other words, this function can only "push" an object from the current thread to another thread, it cannot "pull" an object from any arbitrary thread to the current thread.

int QObject::receivers ( const char * signal ) const [protected]

Returns the number of receivers connected to the signal.

Since both slots and signals can be used as receivers for signals, and the same connections can be made many times, the number of receivers is the same as the number of connections made from this signal.

When calling this function, you can use the SIGNAL() macro to pass a specific signal:

QObject * QObject::sender () const [protected]

Returns a pointer to the object that sent the signal, if called in a slot activated by a signal; otherwise it returns 0. The pointer is valid only during the execution of the slot that calls this function.

The pointer returned by this function becomes invalid if the sender is destroyed, or if the slot is disconnected from the sender's signal.

Warning: This function violates the object-oriented principle of modularity. However, getting access to the sender might be useful when many signals are connected to a single slot.

If the property is defined in the class using Q_PROPERTY then true is returned on success and false otherwise. If the property is not defined using Q_PROPERTY, and therefore not listed in the meta-object, it is added as a dynamic property and false is returned.

Dynamic properties can be queried again using property() and can be removed by setting the property value to an invalid QVariant. Changing the value of a dynamic property causes a QDynamicPropertyChangeEvent to be sent to the object.

Note that QTimer's accuracy depends on the underlying operating system and hardware. Most platforms support an accuracy of 20 milliseconds; some provide more. If Qt is unable to deliver the requested number of timer events, it will silently discard some.

The QTimer class provides a high-level programming interface with single-shot timers and timer signals instead of events. There is also a QBasicTimer class that is more lightweight than QTimer and less clumsy than using timer IDs directly.

Returns a translated version of sourceText, or sourceText itself if there is no appropriate translated version. The translation context is Object with comment (0 by default). All QObject subclasses using the Q_OBJECT macro automatically have a reimplementation of this function with the subclass name as context.

You can set the encoding for sourceText by calling QTextCodec::setCodecForTr(). By default sourceText is assumed to be in Latin-1 encoding.

The table below shows what string is returned depending on the active translation:

Active Translation

n

No Translation

French

English

0

"0 message(s) saved"

"0 message sauvegard?"

"0 messages saved"

1

"1 message(s) saved"

"1 message sauvegard?"

"1 message saved"

2

"2 message(s) saved"

"2 messages sauvegard?s"

"2 messages saved"

37

"37 message(s) saved"

"37 messages sauvegard?s"

"37 messages saved"

This idiom is more flexible than the traditional approach, i.e.,

n == 1 ? tr("%n message saved") : tr("%n messages saved")

because it also works with target languages that have several plural forms (e.g., Irish has a special "dual" form that should be used when n is 2), and it handles the n == 0 case correctly for languages such as French that require the singular. See the Qt Linguist Manual for details.

Instead of %n, you can use %Ln to produce a localized representation of n. The conversion uses the default local, set using QLocal::setDefault(). (If no default locale was specified, the "C" locale is used.)

Warning: This method is reentrant only if all translators are installed before calling this method. Installing or removing translators while performing translations is not supported. Doing so will probably result in crashes or other undesirable behavior.

Returns a translated version of sourceText, or QString::fromUtf8(sourceText) if there is no appropriate version. It is otherwise identical to tr(sourceText, comment, n).

Warning: This method is reentrant only if all translators are installed before calling this method. Installing or removing translators while performing translations is not supported. Doing so will probably result in crashes or other undesirable behavior.

Warning: For portability reasons, we recommend that you use escape sequences for specifying non-ASCII characters in string literals to trUtf8(). Например:

Описание типов

A meta-object contains information about a class that inherits QObject, e.g. class name, superclass name, properties, signals and slots. Every class that contains the Q_OBJECT macro will also have a meta-object.

The meta-object information is required by the signal/slot connection mechanism and the property system. The inherits() function also makes use of the meta-object.

If you have a pointer to an object, you can use metaObject() to retrieve the meta-object associated with that object.

Q_DISABLE_COPY ( Class )

Disables the use of copy constructors and assignment operators for the given Class.

Instances of subclasses of QObject should not be thought of as values that can be copied or assigned, but as unique identities. This means that when you create your own subclass of QObject (director or indirect), you should not give it a copy constructor or an assignment operator. However, it may not enough to simply omit them from your class, because, if you mistakenly write some code that requires a copy constructor or an assignment operator (it's easy to do), your compiler will thoughtfully create it for you. You must do more.

The curious user will have seen that the Qt classes derived from QObject typically include this macro in a private section:

class MyClass : public QObject
{
private:
Q_DISABLE_COPY(MyClass)
};

It declares a copy constructor and an assignment operator in the private section, so that if you use them by mistake, the compiler will report an error.

But even this might not catch absolutely every case. You might be tempted to do something like this:

QWidget w = QWidget();

First of all, don't do that. Most compilers will generate code that uses the copy constructor, so the privacy violation error will be reported, but your C++ compiler is not required to generate code for this statement in a specific way. It could generate code using neither the copy constructor nor the assignment operator we made private. In that case, no error would be reported, but your application would probably crash when you called a member function of w.

If you want to register an enum that is declared in another class, the enum must be fully qualified with the name of the class defining it. In addition, the class defining the enum has to inherit QObject as well as declare the enum using Q_ENUMS().

The property name and type and the READ function are required. The type can be any type supported by QVariant, or it can be a user-defined type. The other items are optional, but a WRITE function is common. The attributes default to true except USER, which defaults to false.

Например:

Q_PROPERTY(QString title READ title WRITE setTitle USER true)

For more details about how to use this macro, and a more detailed example of its use, see the discussion on Qt's Property System.